The present invention relates to a reciprocating piston internal combustion engine having an intake air system and an exhaust gas system, and a fuel injection arrangement comprising at least one injection pump and one injection nozzle; to lubricate the injection pump, lubricating oil can be withdrawn from the internal combustion engine and can be returned to the lubricating-oil system thereof by means of a lubricating-oil return line.
Reciprocating piston internal combustion engines having this general type of arrangement are known, and are conventionally operated with Diesel fuel. However, due to the shortage of oil and the cost thereof, which can be expected to increase still further, fuels which can be synthetically produced, and other alternative fuels, are constantly gaining significance in the operation of internal combustion engines. Furthermore, these fuels also have the advantage of the considerably improved exhaust gas quality in contrast to the internal combusiton engines operated with Diesel fuel. Fuels which can be synthetically produced, or other alternative fuels, especially alcohols such as methanol which have a low boiling point, can be used in varying ways in a completely satisfactory manner in reciprocating piston internal combustion engines having a conventional construction for the aforementioned general type of construction. Thus it has, for example, been proposed to inject methanol via the conventional injection device, and to inject, for example, Diesel fuel via an additional injection device (U.S. Pat. No. 4,368,702, which belongs to the Assignee of the present application). It has also been proposed to provide a special spark plug or glow plug on the internal combustion engine, and to likewise inject methanol via the conventional injection device (East German Patent No. 39 916).
However, when such reciprocating piston internal combustion engines are operated with fuels which have a low boiling point, they encounter the common drawback that the injection pump for injecting the fuel having a low boiling point is connected for lubrication to the lubricating-oil system of the internal combustion engine, as a result of which, due to the unavoidable leakages at the injection pump element, fuel having a low boiling point passes into the lubricating-oil system of the internal combustion engine; due to the prevailing temperatures, especially in the crankcase of the internal combustion engine, the fuel forms an ignitible mixture with the air that exists there. This results in the danger of explosions in the crankcase.
It is therefore an object of the present invention to further develop a reciprocating piston internal combusion engine of the aforementioned general type, while maintaining the advantageous lubricating-oil supply of the injection pump with lubricating oil from the internal combustion engine, in such a way that during operation of the latter with fuel having a low boiling point, the danger of explosions in the crankcase is precluded.